void main()
{
  // transform vertex to clip space coordinates
  gl_ClipVertex = gl_ModelViewMatrix * gl_Vertex;
  gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
  // Copy over the vertex color. 
  gl_FrontColor = gl_Color;
  // transform vertex into texture space to get texture coord
  gl_TexCoord[0] = gl_TextureMatrix[0] * gl_MultiTexCoord0;
}
